Particle Morphology Differentiation on the Basis of Powder Flow Behavior
The morphology of a particle is one of its major characteristics and has a large influence on a powder’s properties such as its flow behavior, tensile strength and internal friction angle. The manufacturing process often greatly influences particle shape. For example, particles produced by different drying technologies (spray drying, drum drying) display different morphologies, which in turn affects flow properties. Knowledge of particle shape is therefore crucial when, for instance, powders have to be pneumatically conveyed and problems occur due to discrepancies in their flow behavior. Until recently, particle morphology was essentially characterized by microscopic methods. However, these techniques do not provide any information on the powder’s flow characteristics. Here, we show that the Anton Paar Powder Cell provides an easy and time-saving method to characterize powder flow behavior. Furthermore, we demonstrate that the test results can give precious informations on particle shape.
Aluminum Oxide Samples
Two aluminum oxide samples (Al2O3) were provided by the Center for Abrasives and Refractories Research and Development (C.A.R.R.D.) in Villach, Austria. One powder consisted of sharp-edged particles, while the other was composed of block-shaped particles. Median particle size was ca. 600 m in both samples. These powders were used as abrasive and filling material as well as for the production of abrasion-resistant materials.
Equipment and Methodology
Experiments were performed with an Anton Paar Modular Compact Rheometer (MCR) equipped with a Powder Cell.
The Powder Cell allows fluidization of powder samples by introducing dry air through a glass frit at the bottom of the measuring cell. The Al2O3 samples were fluidized using a volumetric flow of 50 L/min so that every particle was temporarily moved up and completely surrounded by air. This ensured that possible aggregates and residual tension between particles were removed. Subsequently, we determined Cohesion Strength as a measure of flow behavior. To this end, a 2-blade stirrer was applied, which measured the resulting torque. Torque values were then multiplied by a geometry-specific factor, returning Cohesion Strength values.
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